Three-group zoom lenses are known in the prior art and have been widely used in attempting to provide compact zoom lenses with good correction of aberrations. Recently, digital cameras and video cameras have become highly popular, and in these cameras, small size, high image quality including low distortion and good correction of other aberrations, as well as satisfaction of various conditions connected to the use of solid state image pickup elements in these cameras, have been desired. Additionally, in digital cameras and video cameras, autofocus has become an essential focusing mode and ever faster autofocusing is desired.
The above considerations have resulted in three-group zoom lenses, rather than two-group zoom lenses, being used in such cameras and inner focus or rear focus lenses being used in such cameras because these features enable the zoom lens to weight less and enable the driven lens components to be the ones close to the camera body, which facilitates the drive operation of these cameras. For example, Japanese Laid-Open Patent Applications 2000-284177, 2001-272602, and 2001-296476 disclose three-group zoom lenses that use rear focus and are designed for quick focusing, small size, and high resolution with good aberration correction.
In the zoom lenses described in Japanese Laid-Open Patent Application 2000-284177, the spacing between the second lens group and the third lens group remains nearly constant over the range of zooming while focusing is performed by moving the third lens group in the direction of the optical axis. Therefore, the proper spacings between the second lens group and the third lens group for focusing at infinity must be achievable throughout the range of zooming. Thus, it is difficult to further shorten the overall length of the lens system using a retractable lens when the various requirements of the lens barrel regarding the required movements of the lens groups are considered.
Moreover, the zoom lenses described in all three Japanese published applications listed above require a cam mechanism for jointly moving the second lens group and the third lens group during zooming. Hence there is a restriction on shortening the total length of the lens system in the case of a retractable lens barrel. Accordingly, with the zoom lenses of the three Japanese published applications listed above, it is difficult to greatly reduce the total length of the optical systems with a retractable lens barrel, which limits the compactness of cameras using such zoom lenses when the cameras are not being used.
The present invention relates to a three-group zoom lens that has a zoom ratio of about three times but has a short overall length of the optical system and favorable correction of aberrations. In particular, the present invention relates to a three-group zoom lens that may be used in a digital camera or a video camera and that may be used with a solid state image pickup element.